So I just went to EF and found an MUP fare and it says "THESE FARES APPLY FOR FIRST/COACH CLASS SERVICE" in the fare rules. I swear I've seen others (maybe HUP?) that didn't have the "FIRST/" part in there. Seems like one of those things where DL will screw as many people as they can without downgrade compensation and quietly pay off those who scream loudly enough. I'd also guess that the compensation will be hard to get on the basis of the fact that the coach fare available at the time of purchase is usually not very much below what's paid for the P fare, so if you get to fly F at least one direction, DL will probably argue that you got the value of the fare difference.